The influence of shade, water stress, and root competition on American chestnut regeneration

Caleb Edward Brown, Purdue University

Abstract

There is increasing consensus that regeneration of a variety of commercially and/or ecologically favored forest tree species benefits from maintaining partial canopy cover. American chestnut (Castanea dentata (Marsh.) Borkh.) was once an important element of North American eastern temperate forests before the introduction of a foreign pathogen decimated the population. A blight-resistant, backcross chestnut hybrid has been developed and chestnut reintroduction will occur in part using reforestation under partial canopy. In the first experiment (CHAPTER 2), American chestnut bareroot (1+0) seedlings from three orchard sources (orchards) were grown under one of three light availabilities (high, 76%; medium, 26%; and low, 8% full PAR) and subjected to one of two levels of water availability (well-water and water stressed induced mid-season). In the second study (CHAPTER 3), the effects of overstory and herbaceous root competition on growth and survival of American chestnut and northern red oak (Quercus rubra L.) seedlings planted following midstory removal (14% transmittance) over three years were examined; leaf physiological traits were measured on surviving American chestnut seedlings during the third year. In the first experiment (CHAPTER 2), light availability and water stress interacted to affect many seeding physiological and morphological traits. Seedlings growing under medium and high light wilted at lower leaf Ψ pd (144 and 150% respectively) than low light seedlings. Recovery of relative net photosynthesis (Anet) and stomatal conductance (gs) over a 2-4 week recovery period was greater in low and medium light, Anet (160 and 164%, respectively) and gs (162-181%, respectively), than in high light. Recovery of relative Anet and gs was lower (53-62% and 43-62%, respectively) under high light for one orchard source than the other two, though most other orchard effects were non-significant. As light availability was reduced, light became limiting to the extent that adding an additional stress (in this case water stress) had no impact on a number of growth and morphological traits. In the second experiment (CHAPTER 3), overstory root competition reduced the relative aboveground growth of both species (51-60%). Herbaceous root competition had no effect on seedling growth, yet reduced survival (81%) in northern red oak. American chestnut showed greater net photosynthetic assimilation (8%), stomatal conductance (13%), and leaf N concentration (4%) in the absence of overstory root competition. American chestnut had greater relative aboveground growth compared to northern red oak (112 to 122% for height and DBH, respectively), and its relative height growth was more responsive to the removal of overstory root competition (197%). Results from the first experiment suggest that intermediate light levels provided the most favorable conditions for seedlings to cope with and recover from water stress. The medium and high light treatments imposed in this study apparently improved seedling capacity to maintain leaf turgor under low leaf Ψ pd, while the low and medium light treatments imposed in this study provided enough shade to increase relative Anet and gs recovery, likely due to alleviated harsh environmental conditions. Findings from the second experiment suggest that under partial-canopy conditions, overstory root competition limited seedling growth and physiological development during establishment. Collectively, results from these studies demonstrate both positive and negative aspects of American chestnut development in shaded environments, and also indicate that regeneration of American chestnut under partial canopy is a viable restoration method.

Degree

M.S.

Advisors

Jacobs, Purdue University.

Subject Area

Forestry|Plant sciences

COinS